Throughout the description, the expression “stone” is used to designate any dry cast masonry or dry cast landscaping products such as artificial stones, pavers, edgers, retaining walls, etc. Therefore, the use of the expression “stone” should not be given a restrictive meaning, as it intends to designate a variety of dry cast products.
It is known in the art that artificial products, such as pavers, low walls, etc., may be produced from two widely used casting processes: a wet cast molding process and a dry cast molding process. Using the wet cast molding process, it is possible to produce stones having textures on one or many of their surfaces, thereby giving a more antique and/or natural appearance to the stones. It is worth mentioning that in the field of pavers and stones, the expression “natural” refers to the quality of a surface which has the same properties and or the same geometry as a natural stone found in nature or cut by artificial means such as a splitter in a quarry or the various tools used by a stone cutter or mason; whereas the expression “antique” refers to the wear that is visible on a surface that was weathered by the passage of time. The wear can be caused by the actual aging of a product or by artificial means.
One way to capture the imprint of the natural stone to produce such artificial stones consists in obtaining a mold of one or more natural stones by pouring a resin/fiber material, such as polyurethane, over the natural stone so as to solidify the same in the shape of the stone. Another way to produce such artificial stones consists in scanning a surface of one or more natural stones, and producing molds from the numerical scans. Once the molds are obtained, a wet concrete mixture is poured into the molds and left to dry. After a predetermined period of time, when the concrete mixture is dried, the molds are stripped off from the formed wet cast stones. As previously mentioned, the molds may have textured inner surfaces similar to the surfaces of natural stones for imprinting a texture on top, bottom and/or side surfaces of the wet cast stones. One drawback of using the wet cast molding process to produce stones having an antique look on their top and side surfaces, is that the process is time consuming and costly. Generally speaking, wet cast processes also require longer manufacturing times, and therefore a lower productivity, due to the drying and demolding times, which are considerably longer than comparable dry cast processes.
Dry cast molding, in comparison, offers a number of advantages over wet cast molding. Typically, a dry concrete mixture is poured into individual compartments of a molding frame. The frame resembles a large tray with holes punched through it, with each hole being a compartment. In use, the frame is placed on a plate, creating a temporary bottom to the compartment. Tamper-shoes are used for compacting dry concrete mixture within the individual compartments. Once compacted, the frame is raised relative to the tamper shoes and plate, disengaging the compacted concrete mixture. This vertical de-molding operation is also called stripping. The concrete stones are then transferred to another area for further processing.
The shape of the individual compartments can be designed in a wide range of patterns in accordance with the desired shape of the dry cast stones to be formed. The tamper shoes may be provided with various textured patterns on their surfaces to imprint the same onto the top surfaces of the dry cast stones upon compaction of the dry concrete mixture. These textured patterns can be used to create an antique and/or natural appearance to the top surface of the dry cast stones.
Creating such textures on the sides of dry cast stones, however, is somewhat more difficult. Usually, the individual compartments used for compaction are delimited by flat inner side walls. Therefore, the resulting stones have flat side surfaces having no texture, thus yielding an artificial appearance. Stones having laterally projecting elements, such as interlocking tongues and grooves, can be created in molds with corresponding sliding panels which retract within the mold to allow stripping. The inner walls of the individual compartments may also be designed with vertical recesses or protrusions carved or embossed into the flat surfaces of the inner walls so as to create spacers or interlocking devices on the sides of the dry cast stones. Such designs are limited by the nature of the stripping operation, which is preferably done very quickly once the compacting operation is completed.
Of course, it is also possible to demold the dry cast stones from the molding frame by retracting the inner walls altogether before proceeding with the vertical relative motion between the molding frame and the stones. In that case, the surfaces of the movable inner walls may be provided with natural looking textures (irregular, uneven surfaces). However, implementing retractable inner walls is very complex and costly. It is therefore avoided when possible.
The following US patents disclose prior art techniques developed for manufacturing dry cast products with textured side walls.
U.S. Pat. No. 5,078,940, issued Jan. 7, 1992 to Sayles, describes a mold for making a concrete block having a roughened texture on one side. A set of projections and a reinforcing mesh along an inner wall of the mold are provided to retain a portion of the mold material inside the mold during stripping, thereby shearing off that portion during stripping and creating a fractured, roughened texture on one side.
U.S. Pat. No. 6,209,848, issued Apr. 3, 2001 to Bolles et al., describes another mold for making a concrete block having a roughened texture wherein an inwardly facing lip is provided along the lower edge of one of the walls. As the block is removed from the mold, the lower lip acts to scrape the mold material, thereby leaving a roughened surface. Similarly, U.S. patent application Ser. No. 10/091,039, published as 2003/0164574 on Sep. 4, 2003, describes a mold for texturing a concrete block wherein an inner surface comprises projections extending into the mold cavity for scoring the block during stripping.
U.S. patent application Ser. No. 10/307,785, published as 2004/0104511 on Jun. 3, 2004, describes a mold for texturing a concrete block providing a mesh encircling one of the mold sidewalls. The mold material forms to the mesh during compaction, and is retained to the surface of the mesh during stripping. The mesh is operable to rotate around the wall as the block is demolded, thereby discharging a portion of the mold material and creating a roughened surface.
U.S. Pat. No. 4,761,095, issued Aug. 2, 1998 to Bartlechner, describes a paving stone having vertical ridges disposed along its lateral sides. These side surfaces are aimed at anchoring adjoining stones against lateral shifting and displacement.
However, while each of these techniques may aid in creating a non-uniform side surface, they also generally provide molds which score, mark or otherwise fracture a side of the compacted block. Therefore, and according to some people, the side surfaces obtained with these techniques often still have an artificial look.
As such, there exists a continued need for improved methods and apparatuses for producing dry cast masonry or landscaping products having textured side surfaces.